PHYLOGENIC STAGE OF THE GASTROPODA 475 



placed. Correctly referred, the faunas appear as follows: Asso- 

 ciated with the brachiopod Lingulepis and the trilobites Agraulus 

 and Dicellocephalus in the Dresbach formation occurs the Hyo- 

 lithes primordialis Hall, widely distributed seaward, while at the 

 seashore, as described, with it are the gastropods Tryblidium 

 (Metoptoma), Hypseloconus, and Scaevogyra. The succeeding 

 Franconia sandstone, at Taylor's Falls, Minn., has the same 

 genera of gastropods. This may be taken as the equivalent to 

 the top of the Potsdam of New York. 



The next succeeding formation, the St. Lawrence, contains in 

 a trilobite zone at Osceola, Wis., near Taylor's Falls and only a 

 mile or two from the then seashore, Tryblidium sp.?, Pleurotomaria 

 sweeti Whitf., Miirchisojiia putilla Sar., and Bellerophon Mitiqiiatus 

 Whitif. At another point on the Blue Earth River, Minnesota, 

 which is near another shore of that time, Mure his onia putilla Sar., 

 was found either in the base of the Jordan sandstone, or as I 

 suspect, now really the top of the St. Lawrence formation. Also 

 Raphistoma 7ninnesotense Owen and Ophileta alture?isis Sar., occur 

 in the same matrix. R. minnesotense Owen also comes from Red 

 Wing, Minn., which is distant from the shore. Next, the coarse 

 Jordan sandstone is practically the unfossiliferous basal sand of 

 the Oneota dolomite, and this one is the supposed Lower Calcif- 

 erous sand rock equivalent. Fossils generally have been oblit- 

 erated in the Oneota, but a few Lingulas, and two fragments of 

 trilobites, have been found, with a number of gastropods, which 

 are the same species as those enumerated from the St. Lawrence 

 formation, with also others of the genera Straparollus, Holopea, 

 and Ophileta. Cephalopods also occur, of the genera Ascoceras, 

 Piloceras, Orthoceras, et. al. The superjacent Shakopee dolomite 

 (Upper Calciferous) contains only gastropods and cephalopods, 

 as far as known, and, excepting the genus Subulites, they are 

 species very similar to, though not identical with, those of the 

 Oneota,^ 



In all these localities and horizons where the gastropods 

 occur there are evidences of shallow water to be found, con- 



'F. W. Sardeson, "The Fauna of the Magnesian Series," Bulletin of the Min- 

 nesota Academy of Natural Science, Vol. IV (1896), pp. 92-105. 



